An electric vehicle includes a traction battery system. Certain traction battery systems include batteries connected in parallel with one another. In some of these battery systems, the batteries are of different chemical types from one another. For instance, a traction battery system may have two different chemical type batteries connected in parallel with one of the batteries being a lead-acid battery and another battery being a lithium-ion (Li-ion) battery. The batteries have different dynamic characteristics and impedances due to the different chemistries. It may be advantageous to predict the responses of the batteries to a demanded current to be outputted by the battery system.